We developed a germ-cell specific monoclonal antibody (MA-24) against spermatozoa plasma membrane (Naz et al., Science 225:342, 1984) which blocked human sperm penetration of zona-free hamster ova and inhibited in vitro fertilization of mouse ova by murine sperm without causing agglutination or immobilization of sperm. It recognized a single glycoprotein of testicular origin present on postacrosomes, midpieces and tails of sperm. This fertilization antigen (FA-1) has been isolated from human and murine germ cells using MA-24 immunoaffinity chromatography (Naz et al., Proc. Natl. Acad. Sci., USA, 83:5713, 1986). The overall objective of this project is to characterize sperm-specific antigen (FA-1) and investigate its role in fertilization, embryonic development, implantation and postimplantation fertility in mice. FA-1 will be isolated from murine testes in large amounts by using immunoaffinity chromatography and further purified and characterized for its molecular identity, subunit structure, amino acid contents and carbohydrate composition. The antigenic fragment (polypeptide) of the FA-1 will be isolated by using high performance immunoaffinity chromatography. FA-1 will be checked for its immunogenicity and monoclonal antibodies will be raised reacting against its various antigenic determinants. The fate of antigen after fertilization will be investigated. It will be checked whether MA-24 is directed against carbohydrate or polypeptide portion of the antigenic molecule. We will check the role of FA-1 in fertilization and post-fertilization fertility. We will investigate the cross-reaction of FA-1 with sera from immunoinfertile patients. Besides enabling us to define the molecular events underlying fertilization, embryonic development, and implantation, this project will provide a basis for specific methods for diagnosing and managing involuntary immunoinfertility in humans and development of an anti-sperm contraceptive vaccine.